Point-of-care ultrasound in internal and emergency medicine: from basics to training and implementation

Thesis

Reference

Point-of-care ultrasound in internal and emergency medicine: from basics to training and implementation

GROSGURIN, Olivier

Abstract

Growing doubts regarding history and physician examination (HPE) value, coupled with recent advances in ultrasound technology and miniaturization offered conditions promoting the gradual advent of point of care ultrasound (POCUS). POCUS is meant to answer specific, basic and usually binary clinical questions to address specific hypotheses in a timely manner in order to immediately guide treatment and/or orientation at bedside. In internal and emergency medicine, POCUS is used for simple diagnostic purposes. Indeed, in complement to HPE, POCUS allows identification of cardiac, pleuro-pulmonary, abdominal and vessel abnormalities leading to a straightforward diagnosis. In addition, multimodal POCUS examination is performed in acute distress syndromes (e.g. acute respiratory and/or circulatory failure, cardiac arrest, multiple trauma) where it narrows differential diagnosis and shortens time to diagnosis and/or treatment according to recent evidence. Moreover, insertion of POCUS guided central and peripheral venous catheters has been extensively proven to be safer than historical non US guided procedures. Other semi-invasive [...]

GROSGURIN, Olivier. Point-of-care ultrasound in internal and emergency medicine:

from basics to training and implementation. Thèse de privat-docent : Univ. Genève, 2021

DOI : 10.13097/archive-ouverte/unige:155065

Available at:

http://archive-ouverte.unige.ch/unige:155065

Disclaimer: layout of this document may differ from the published version.

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Clinical Medicine Section Department of Medicine and Department of Acute Medicine

"Point-of-care ultrasound in internal and emergency medicine: from basics to training and implementation"

Thesis submitted to the Faculty of Medicine of the University of Geneva

for the degree of Privat-Docent by Olivier GROSGURIN

Geneva

2021

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TABLE OF CONTENTS

Chapters/sections Page

Summary

1. Introduction

1.1 POCUS definition

1.2 POCUS history

2. POCUS applications and their benefits

2.1 Diagnostic

2.1.1 Heart

2.1.2 Lung

2.1.2.1 Pulmonary oedema 15

2.1.2.2 Pneumonia 15-18

2.1.2.3 Pleural effusion 18

2.1.2.4 Pneumothorax 19-21

2.1.3 Abdomen

2.1.3.1 Ascites 22

2.1.3.2 Cholecystitis 22-23

2.1.3.3 Bladder distension and hyronephrosis 24

2.1.3.4 Abdominal aortic aneurysm 24

2.1.4 Veins

2.2 Acute syndromes

2.2.1 Multiple trauma and E-FAST protocol

2.2.2 Acute respiratory failure and the BLUE protocol

2.2.3 Acute circulatory failure and the RUSH protocol

2.2.4 Cardiac arrest and the CAUSE protocol

2.3 Procedure guidance

2.3.1 Central venous catheterization

2.3.2 Peripheral venous catheterization

2.3.3 Thoracentesis and paracentesis

2.3.4 Lumbar puncture

2.4.5 Other procedure guidance

3. POCUS training

3.1 POCUS general training structure

3.1.1 POCUS initiation

3.1.2 POCUS practical training

3.2 POCUS specific curricula

3.2.1 POCUS Internal and Emergency Medicine curricula

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Table of contents (continued)

4. POCUS Implementation

4.1 Communication of POCUS curriculum

4.2 POCUS local referents

4.3 Collaboration with other “ultrasonographers”

4.4 POCUS and material

4.5 POCUS and finances

4.6 POCUS scientific evidence of impact

4.7 Geneva: POCUS implementation in Internal and Emergency

Departments

50-53

5. General conclusion

6. Acknowledgments

7. References

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SUMMARY

Growing doubts regarding history and physician examination (HPE) value, coupled with recent advances in ultrasound technology and miniaturization offered conditions promoting the gradual advent of point of care ultrasound (POCUS). POCUS is meant to answer specific, basic and usually binary clinical questions to address specific hypotheses in a timely manner in order to immediately guide treatment and/or orientation at bedside.

In internal and emergency medicine, POCUS is used for simple diagnostic purposes. Indeed, in complement to HPE, POCUS allows identification of cardiac, pleuro-pulmonary, abdominal and vessel abnormalities leading to a straightforward diagnosis. In addition, multimodal POCUS examination is performed in acute distress syndromes (e.g. acute respiratory and/or circulatory failure, cardiac arrest, multiple trauma) where it narrows differential diagnosis and shortens time to diagnosis and/or treatment according to recent evidence. Moreover, insertion of POCUS guided central and peripheral venous catheters has been extensively proven to be safer than historical non US guided procedures.

Other semi-invasive procedures such as ascites and pleural fluid punctures, and more recently lumbar puncture have also shown to be safer with US guidance.

The added clinical value of POCUS intimately depends on the quality of POCUS training and implementation. Usual training structure comprises three distinct steps: POCUS initiation, POCUS practical training and POCUS certification. POCUS initiation consists in theory acquisition through didactic lessons or growing more efficient Web-based content and practical ultrasound “hands on”

sessions (healthy volunteers and/or patients), aiming at proper image acquisition. This initiation should be as early and as accessible as possible, automatically integrated in regular Emergency Medicine and Internal Medicine postgraduate education. POCUS supervised practical training follows; it is very demanding for trainers and trainees, but stands as a determinant factor to concretely build competency and to rigorously anchor POCUS in bedside evaluation.

Successful POCUS implementation needs overt and regularly repeated clarification of its scope of practice, thus offering a delineated frame of practice to its users and a reassuring message to other institutional ultrasound providers. Besides that, current developments towards improved device simplicity and maneuverability contribute to POCUS efficient implementation. In addition, it is crucial to rely on enough well-trained referents in the process of POCUS integration. They are essential to promote, teach and honestly assume POCUS activity.

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Material, teaching, supporting and supervising resources are progressively available to ground POCUS as an additional truly reliable pillar of HPE. Its humble though determined implementation, alongside HPE and other imaging procedures, should be supported without restriction.

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1. Introduction

For centuries history and physical examination (HPE) have been the cornerstone of the diagnostic process in medicine. Some authors still consider it as a highly powerful diagnostic tool. Elder et al.

conducted a large international survey among more than 2660 doctors and HPE was deemed "almost always valuable" in 70% of cases.¹ Furthermore, HPE seems to allow clinicians to identify correct diagnostic more than 80% of the time,² especially if recognized accurate elements of HPE are taken into account.^2,3 Moreover, beyond the diagnostic purpose, HPE definitely plays a major role in the relationship between patients and physicians: it is an opportunity to demonstrate a real interest in patients physical issues, thereby building trust and an empathetic relationship.^4,5 On the other hand, HPE also has detractors. Worrisome data have been published on reliability of HPE regarding evaluation of circulatory shock and/or more complex hemodynamic disturbances,^6,7 heart murmurs⁸ or even pneumonia.⁹ Several arguments are regularly mentioned to explain these disappointing performances of HPE: time spent with patients carrying out HPE can be as low as 12% of duty hours,¹⁰ HPE teaching is sometimes declared insufficient¹ and is progressively perceived as an old fashioned procedure given the recent advances in medical technology.¹¹ In the French speaking part Switzerland, a survey conducted among Emergency Medicine (EM) and Internal Medicine (IM) physicians showed that confidence in clinical signs to detect ascites and/or pleural effusion is limited; in this this study we also showed that focused ultrasound (US) is a growing alternative to detect these free fluids (Saudan A., Leidi A., and Grosgurin O., Use and Confidence in Physical Examination and Point-of-Care Ultrasonography for Detection of Abdominal or Pleural Free Fluid. A Cross-sectional Survey, publication in progress).

1.1 POCUS definition

The debate on the value and place of HPE, coupled with recent advances in medical ultrasound technology, has provided ideal grounds for the emergence of Point of Care Ultrasound (POCUS), also regularly termed focused, clinical, bedside or goal directed US. POCUS is defined by the utilization of an US device by the clinician him-or herself, at the point of care (bedside). The aim of POCUS is to:

 1. complete HPE towards improved diagnostic accuracy

 2. immediately guide treatment

 3. monitor critical situation (mainly hemodynamic and respiratory failures)

 4. guide invasive procedures (central venous catheterization for example)

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POCUS is designed to answer specific, basic and usually binary questions to address specific hypotheses in a timely manner, such as:

 “Is there a pericardial effusion explaining hypotension?” or,

 “Is there hydronephrosis explaining acute renal failure?”

POCUS images are immediately integrated into the clinical reasoning of the physician and help to guide ongoing therapy without delay.¹² POCUS is however not meant to substitute conventional comprehensive radiologist or cardiologist’s US: these specialized US examinations aim at completely describing organs or systems and pathological findings in details, offering more precise information useful to final diagnostic elaboration. Their usefulness is unique and not challenged by POCUS, but they conceptually cannot be used to pilot immediate therapy as they are usually performed by a physician not directly taking care of the patient. In addition they imply delay in performing and interpreting the examination and delay in the communication of their results to the physician in charge of the patient.

1.2 POCUS history

US development started in the beginning of the 20^th century with transducers being used to spot submarines during World War I. It was then integrated in medicine in the late 1950s, first by obstetricians.¹³ US was then progressively integrated into clinical practice by radiologists and cardiologists. POCUS made its first appearance in the 1980s in critical care medicine (CCM) and EM. A few years later, a first statement supporting POCUS was published by the American College of Emergency Physicians (ACEP) and since then guidelines are regularly updated for POCUS use.¹⁴ In parallel, the Focused Assessment with Sonography in Trauma (FAST) was elaborated by surgeons, aiming at visualizing blood in the abdomen and/or pericardium following blunt trauma.¹⁵ This protocol acts as a milestone in POCUS history, it is currently supported by the Advanced Trauma Life Support providers and used around the world in EM.¹⁶ The American College of Chest Physicians (ACCP) and the Société de Réanimation de Langue Française (SRLF) joined in 2009 to establish the first international position paper on POCUS competence in critical care settings.¹⁷ In the meantime POCUS use extended to many other specialties, including internal medicine.¹⁸ This recent and massive spreading of POCUS use has been supported by progress in digitalization and technology that allowed

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the development of small, high-quality and highly portable devices.¹⁹ Technological progress and historical important steps in US and POCUS evolution are summarized in figure 1.

Figure 1. History of US and POCUS. Reproduced with permission of Internal and Emergency

Medicine Journal, Leidi A, Grosgurin O.

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Given this rapidly growing utilization, questions have been raised about the precise scope and the necessity of a quality control in POCUS. In addition, a consistent body of research is now available in POCUS and this in itself implies a need for frequent and rigorous synthesis of evidence. In this context, the present narrative review aims at detailing the most recent and pertinent data in terms of POCUS usual applications and their benefits, POCUS training and finally POCUS implementation in medical culture and practice.

Regarding methodology, the literature research of this narrative review was conducted basically using three web-based search engines: Google Scholar (https://scholar.google.com), Pubmed (https://pubmed.ncbi.nlm.nih.gov) and ACCESSSS (https://www.accessss.org/). No specific filter regarding period of publication was applied. Search terms were: “POCUS”, “bedside ultrasound”,

“focused ultrasound”, “clinical ultrasound”, “goal directed US”, completed by fields of interest such as

“applications”, targeted organs (for example heart, lung, abdomen), “protocol”, “training”, “teaching”,

“curriculum” or “implementation”. When the title of the retrieved article was relevant, full reading was performed, provided that the abstract was also deemed relevant. Selected references of articles and some “related articles” were also analyzed.

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2. POCUS applications and their benefits

POCUS utilization can be classified into three broad categories: ¹⁴ 1. Diagnostic

2. Acute distress syndromes (e.g. acute respiratory failure, blunt trauma for example) with multimodal POCUS protocols

3. Procedure guidance

In the following sections major POCUS applications integrated into clinical practice in IM and EM will be described.

2.1 Diagnostic

Updated diagnostic performances of POCUS are available in table 1. Some of the most frequent diagnostic applications in IM and EM are described in details below.

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Table 1. Diagnostic performances of POCUS in different applications. Reproduced with

permission of Internal and Emergency Medicine Journal. Leidi A, Grosgurin O.

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2.1.1 Heart

IM and EM physicians are exposed on a daily basis to clinical situations where real-time evaluation of the heart can bring critical information regarding diagnosis and treatment. Bedside focused cardiac ultrasound (FCU) is therefore progressively becoming essential to their clinical practice. Even if IM and EM clinician’s formal training in echocardiography is definitely less advanced than that delivered to cardiologists or professional sonographers, it is now widely recognized that FCU can offer useful and reliable sonographic information, provided that a limited scope of practice is respected and sufficient training has been achieved. Even though some conflicting opinions and data have been published on the subject, a training with a 2-day course followed by performing and interpreting >25 FCU examination has generally been shown to induce good accuracy of FCU,^20-23 in particular if analysis is restricted to the easiest views to obtain (parasternal and subcostal views).²⁴ Once again, in order to keep FCU useful and safe, the scope of FCU must be restricted to specific clinical situations, the goal being to qualitatively (or semi-quantitatively) identify or exclude specific cardiac abnormalities that are both easy to find and immediately useful for early patient management. These cardiac focused parameters are principally:

1. Left ventricular function: appropriate evaluation of systolic function allows clinicians to explain various clinical pictures and to rapidly adjust treatment, particularly when facing hemodynamic and/or respiratory distress. After focused training in echocardiography, EP have been shown to accurately estimate left ventricular systolic function with qualitative visual analysis (when compared to cardiologists, Spearman or Pearson correlation coefficient R >

0.85),^25-27 and even with some more sophisticated semi-quantitative analysis such as E-point Septal Separation (EPSS) or Mitral Annular Plane Systolic Excursion (MAPSE).^28,29

2. Pericardial effusion (PEf): because of the potential for rapidly occurring hemodynamic instability, immediate and accurate identification of PEf is essential for clinicians potentially exposed to acute life threatening situations, just as EM and IM physicians. Even after limited training EP are highly reliable in evaluating the presence/absence of PEf.³⁰

3. Right ventricule (RV) to the left ventricule (LV) size ratio: in the acute setting detection of right ventricular dilation can be of critical importance, particularly if circulatory failure is present, as it raises the probability of an acute pulmonary embolism (PE) and is a severity marker of PE.³¹ Given the fact that massive PE-associated mortality occurs mainly during the first hour after admission and that early treatment can have a positive impact, prompt identification of RV dilation is mandatory in acute medicine.³² Moderately but adequately trained EP have been shown to accurately identify RV dilation (RV to LV ratio of >1), with

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specificity and positive predictive value of more than 90% when compared to gold standard consultative echocardiography performed by cardiologists. Sensitivities are nevertheless less encouraging with values between 25% and 50%, subtle signs of RV overload being more difficult to identify. ^31,33

4. Inferior vena cava (IVC) evaluation: in acute medicine evaluation of volume status has obvious implications in patient’s early management and traditional clinical “volemia” findings have particularly limited value.³⁴ The contribution of POCUS to assessment of volume status and fluid responsiveness by measurement of IVC diameter and IVC “collapse index” (end expiratory IVC diameter-end inspiratory IVC diameter/end expiratory IVC diameter x 100) has been extensively studied over the past years. Recent pooling of studies shows limited ability of POCUS to predict fluid responsiveness (sensitivity 0.63 (95% confidence interval [CI]: 0.56–

0.69), 0.73 (95% CI: 0.67–0.78)), especially in spontaneously breathing patients.³⁵ Some data are encouraging yet, in particular when extreme cut offs of IVC diameter or collapse index are used to interpret volemia.^36,37 Nevertheless, extreme cut offs are probably also reliably identified by clinical findings alone. Consequently, IVC evaluation with POCUS, like many other POCUS applications, is thus to be integrated with other clinical findings in clinical reasoning as US images of IVC must be interpreted with particular caution.

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2.1.2 Lung

Until recently lung ultrasound (LUS) was not considered as an effective diagnostic tool due to the air- filled nature of the lung tissue, interfering with ultrasound wave propagation. Nevertheless intensivists and EP lately observed that pleural changes such as air or fluid filling can create specific ultrasound images. Moreover, beyond the pleural space, changes in fluid and/or air volume, inflation or impedance of the lung tissue can alter ultrasound signal in particular ways; these artefactual images are actually reflecting ordinary pathological conditions such as lung edema or lung consolidation for example (figure 2).^38-40 Even if LUS has been largely developed by critical care providers, it does not yet

“belong” to any specialty and is a recent approach deserving here a specific development on its established diagnostic performances and the original sonographic images that will be illustrated in the next sections.

Figure 2. (A-C) The concept of lung ultrasound as a densitometer: different ultrasound

patterns for different levels of lung aeration. Reproduced with permission of Internal and

Emergency Medicine Journal, Leidi A and Grosgurin O.

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2.1.2.1 Pulmonary oedema

The echographic hallmark of cardiogenic oedema are B-lines (figure 2B), defined as discrete laser-like vertical hyperechoic reverberation artefacts moving along with lung sliding that arise from the pleural line and extend to the bottom of the image. They extend vertically to the lower screen end without fading and move in synchronization with breathing movements. The presence of more than 2 B-lines in an intercostal space is an indication of interstitial syndrome.⁴¹ Several scanning protocols exist for B-lines quantification. Recently in Geneva we conducted a study aiming at comparing a 8-point to a 28-point LUS protocols: the 8 point protocol was shown to be more reproducible and timesaving than the 28-point protocol (Leidi A., Grosgurin O. et al, Eight versus Twenty-eight Point Lung Ultrasonography in Moderate Acute Heat Failure: a prospective comparative study, publication in preparation). These results are in line with similar very recent studies on the same research question.^42,43

In a recent meta-analysis, LUS with recognition of B-lines has been suggested to be superior to chest X-ray for the detection of pulmonary oedema, in particular with sensitivities of 0.88 (95%Cl, 0.75-0.95) and 0.73 (95%CI, 0.70-0.76) respectively for LUS and chest X-ray (gold standard: acute decompensated heart failure diagnosis by a clinical expert, or a combination of echocardiography findings and brain- type natriuretic peptide criteria).⁴⁴ Tailored therapy with LUS in acute heart failure is also probably positively affecting clinical course and hospital length of stay (LOS).⁴⁵ Persistence of B-lines at discharge was furthermore shown to convincingly correlate with re-admission risk.^46,47 In Geneva we are planning a randomized controlled trial to evaluate the impact of LUS on readmission rate of patients admitted with acute heart failure (Leidi A., Grosgurin O., Intervention reducing acute readmission rate with lung ultrasound). LUS is now identified as an essential tool to detect pulmonary oedema and guide treatment and is consequently integrated, with the evaluation of IVC collapsibility, in volume assessment.

2.1.2.2 Pneumonia

LUS typical signs suggesting pneumonia are:

1. Tissue-like consolidation (hepatization), with bright white dots (air) (figure 3) 2. Branching hyperechoic lines called air bronchograms (figure 3)

3. Irregular border at the interface with normal lung : shred sign (figure 4)

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4. Focal interstitial pattern with B-lines (figure 5B), subpleural lesions defined as hypoechoic nodules of different shapes (figure 5C), pleural line abnormalities with pleural thickening and/or coarse aspect of the pleural line with extinction of lung sliding (figure 5D)

5. Associated pleural effusion (figure 6)

6. Intact vessels (allowing distinction with infarction)

Individual performances of these LUS signs are not known but overall diagnostic utility has already been evaluated. Diagnostic studies evaluating LUS have reported a sensitivity of 80 to 90% and a specificity of 70 to 90%, with a pooled AUC of 0.93 for the diagnosis of pneumonia. ^48,49 These studies included community and hospital-acquired pneumonia and used various reference standards such as final diagnosis of pneumonia at discharge and occasionally CT-scan.^50,51

Figure 3. Consolidation (yellow arrow), bright dots (green arrow), air bronchogram (blue

arrows). Liver (red arrow). With courtesy of Dr A Leidi.

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Figure 4. Shred sign (black arrows). Lower lobe (LL) consolidation, pleural effusion (E), spleen (S). Reproduced with permission of Chest, Liechtenstein D and al.

f Chest

Figure 5. Focal interstitial pattern (figure 5B), subpleural lesions (figure 5C), pleural line

abnormalities (figure 5D). Reproduced with permission of Journal of thoracic disease, Liu X

et al.

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In studies using CT-scan as a reference standard, LUS had higher sensitivity than CXR, with similar specificity ⁵¹⁵³. Therefore LUS can already be seen as a promising alternative diagnostic tool, given its immediate availability and its non-irradiating nature. In our center we are planning to conduct a multicenter prospective pragmatic study comparing in each patient with suspicion of pneumonia the diagnostic performance of CXR, LUS and low dose CT-scan (Prendki V. et al,. Low-dose CT comPared to lung ultrasonography vs standard care for the diagnosis of pneumonia: a multicenter randomized controlled study. Swiss national science foundation number 32003B_197398. Recruiting starts in summer 2021)

2.1.2.3 Pleural effusion

In LUS pleural effusion is first looked for in both lateral chest wall just above the diaphragm. It appears as a dark anechoic space displacing the lung superior to the diaphragm (figure 6).⁵⁴ Recognition of pleural effusion by the clinician has diagnostic but also direct practical therapeutic importance since evacuation of fluid can be ultrasound-guided (see further section 2.3.3). The development of POCUS to detect pleural effusion has emerged in the 1960s and has kept maturing ever since. Its performances to identify fluid in the pleura have been compared to other diagnostic modalities (CT, chest X-ray) and POCUS performed by various type of operators (radiologists, intensivists, internists) has been shown in a recent meta-analysis to be more accurate than chest X-ray to detect pleural effusion, with pooled sensitivity of 0.94 (95% CI: 0.88-0.97; I2= 84.23, p<0.001) and pooled specificity of 0.98 (95% CI: 0.92- 1.0; I2= 88.65, p<0.001), while sensitivity and specificity of chest radiography were 0.51 (95% CI: 0.33- 0.68; I2= 91.76, p<0.001) and 0.91 (95% CI: 0.68-0.98; I²= 92.86, p<0.001).⁵⁵ Bedside LUS can detect pleural effusions as small as 20 ml compared to a lower detection limit between 50 and 200 ml for upright chest radiography, this latter image modality being sometimes difficult to obtain in the acute setting.^54,56

Figure 6. Pleural effusion. With courtesy of Dr A. Leidi

White arrow: diaphragm Yellow arrow : vertebral column

White circle: pleural effusion

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2.1.2.4 Pneumothorax

Under normal conditions, when the probe is placed in the longitudinal plane, the parietal pleura can be seen as a thin echogenic pleural line joining the inferior borders of two adjacent ribs (figure 8A);

when the parietal pleura adheres to the visceral pleura, this line is moving with active or passive respiration. This movement is called “lung sliding” (see below). A classic normal view also contains A- lines that are reverberation artefacts visualized as horizontal lines repeating the pleural line below it (figure 8B).

Figure 8. A. The pleural line (yellow arrow), local personal images and B. A-lines (horizontal lower arrows), ribs (2 vertical higher arrows), pleural line (yellow arrow), with permission of Chest, Lichtenstein et al.

In pneumothorax (PTX) air is located within the pleural space. This condition impedes spreading of the ultrasonographic beam further down through deeper lung structures and would in principle preclude the use of any LUS application. However, a few dynamic sonographic artefacts actually allow detection and quantification of PTX; these signs are easy to recognize in a reliable way even by non-experienced LUS providers⁵⁷ and should be properly combined to obtain the highest

performance of this technique.⁵⁸ Four sonographic PTX signs are classically described:

1. Lung sliding: lung sliding should be checked first, as its presence safely rules out PTX.^59,60 As mentioned above, lung sliding refers to the movement of the pleural line along with respiration, indicating that both pleural layers (visceral and parietal) are adherent to each other. In the case of air irrupted between these layers, pleural line can still be visualized but does not move anymore. M mode can be used to confirm the absence of lung sliding: the image shows rigorously horizontal lines (“barcode sign”) reflecting movement absence below the pleural line (figure 9). However the absence of lung sliding does not necessarily confirm

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PTX, as some other conditions like atelectasis, pulmonary contusion, ARDS and pleural adhesions can induce motionless pleural line.⁵⁸ Some other signs should then be searched for when lung sliding seems absent.

Figure 9. A. M Mode in normal lung: the image shows horizontal lines above the pleural line (arrow) and granular appearance deep to the pleural line. B. M Mode lung in PTX: horizontal lines are present above and under the pleural line (arrow) reflecting immobility. With courtesy of Dre C. Cantero

A B

2. B-lines: as mentioned above (figure 2B) B-lines have their origin on the pleural line and result from the presence of fluid in the interlobular septa and interstitial syndrome. Their presence is dependent on the integrity of the pleural line (adherence of both pleura). Their signification regarding suspicion of PTX is therefore indirect: the presence of B-lines proves the adherence of visceral and parietal pleura and thus safely rules out PTX. ⁶¹

3. Lung pulse: impulse generated by cardiac mechanical activity can sometimes be transmitted through lung consolidations and/or atelectasis to the pleura. It is then visualized as vertical motion of the pleural line synchronous to cardiac rhythm. In case of PTX, air trapped in the pleural space impedes movement transmission to the parietal pleura. Thus, in PTX both lung sliding and lung pulse are absent.⁵⁸

4. Lung point: facing a constellation of the above mentioned signs suggesting PTX (absence of lung sliding, absence of B-lines, absence of lung pulse), diagnostic confirmation can be obtained by visualization of lung point. Lung point refers to a point of the chest wall where normal image of respiration (lung sliding) is found again and intermittently “erase” the

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standstill pleural line, corresponding to the point where both pleura are in intimate contact with one another again (figure 10). Although its sensitivity is modest (75%), lung point identification has a specificity of 100%.⁶²

Figure 10. Lung point. Yellow arrows. Local personal images.

LUS can be used in various clinical scenarios to detect PTX, from cardiac arrest searching for tension PTX to suspicion of post-procedural PTX. It is now well established that LUS outperforms chest radiography for the detection of PTX: irrespective of the etiology and using mainly lung sliding and B- lines as sonographic signs, sensibility of LUS and chest radiography was respectively 90.9% (95% CI, 86.5-93.9) and 50.2% (95% CI, 43.5-57.0) and specificity was 98.2% (95% CI, 97.90-99.0) and 99.4%

(95% CI, 98.3-99.8) in a meta-analysis pooling the results of 8 studies (1048 patients) in 2012.⁶³

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2.1.3 Abdomen

Abdominal ultrasonography is a complex field and once again POCUS scope should focus on binary answers to simple questions. The most frequent and relevant applications of POCUS regarding abdomen examination in IM and EM are:

 detection of ascites

 diagnostic of cholecystitis

 diagnostic of bladder distension, hydronephrosis and nephrolithiasis

 diagnostic of abdominal aortic aneurism

Performances of POCUS regarding these diagnoses will be described here. Of note, evaluation of the vena cava has been described above in chapter 2 (“Heart” section) and abdominal views included in E- FAST (Extended Focused Assessment with Sonography in Trauma) protocol will be described further in chapter 2.2.1 (acute distress syndromes).

2.1.3.1 Ascites

Detection of ascites (fluid in the peritoneal cavity) has important diagnostic and therapeutic implications since fluid can be identified but also removed with the assistance of POCUS imaging. Even within moderate-experienced hands ultrasonography allows detection of fluid volume less than 100 ml whereas physical examination accuracy for the detection of ascites is estimated to be < 60%.⁶⁴ POCUS-guided evacuation of ascites by emergency physicians is significantly more successful (95%) as compared with paracentesis performed with a traditional method (61%, p = 0.0003),⁶⁵ with reduced complications and costs.⁶⁶

2.1.3.2 Cholecystitis

Abdominal pain is one of the most frequent main complaint in the emergency department (ED). EP’s autonomy in right upper abdominal pain work up competencies might therefore have a significant impact on EP decision making and thus on ED flow of these patients. Suspicion of cholecystitis results from the combination of history, physical, laboratory and radiological findings. As shown in a recent meta-analysis none of these findings is specific or sensitive enough to individually rule in or out cholecystitis. Pooling the heterogeneous results of 4 studies, POCUS performed by moderate-

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experienced EP (or EP with unknown levels of experience) for the detection of cholecystitis showed sensitivity of 86% (range = 78%–94%) and specificity of 71% (range = 66%–76%).⁶⁷ Moreover, in a comparative study ultrasonography performed either by EP with various levels of POCUS training or by radiologists was found to be similar in terms of sensibility and specificity in a convenient sampled observational study (POCUS: sensitivity 87 % (95% CI : 66% - 97%), specificity 82 % (95% CI : 74% - 88%);

radiology ultrasonography : sensitivity 83 % (95% CI : 61% - 95%), specificity 86 % (95% CI: 77% - 92%).⁶⁸

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2.1.3.3 Bladder distension and hydronephrosis

Due to low specificity (50%) of physical examination, US has become an essential tool to assess bladder distension and avoid unnecessary catheterization.⁶⁹ Sensibility and specificity of POCUS for the detection of bladder retention among internists with limited POCUS experience is excellent.⁷⁰ Nurses with short training have also been recognized as highly accurate to establish this diagnosis.⁷¹

Bedside sonographic evaluation of kidneys and proximal urinary tract to binary confirm or exclude hydronephrosis is now definitely part of the initial diagnostic strategy in suspicion of nephrolithiasis and in acute renal failure. Overall accuracy of POCUS to detect hydronephrosis and nephrolithiasis was moderate in a recent meta-analysis pooling the results of five studies (sensitivity: 70.2% (95%

confidence interval [CI] = 67.1%–73.2%, specificity: 75.4% (95% CI = 72.5%–78.2%), but it is significantly improved in moderate or greater hydronephrosis,⁷² as well as by brief training sessions and early continuous supervised practice by experienced POCUS providers.^73,74 It has even been shown to be equivalent to radiologist’s ultrasound accuracy for the detection of nephrolithiasis in a large randomized study, with significant reduction of ED LOS.⁷⁵

2.1.3.4 Abdominal aortic aneurysm

Ruptured abdominal aortic aneurysm (AAA) is usually fatal with mortality rates above 80% ; unfortunately in the vast majority of cases, AAA remains asymptomatic until rupture.⁷⁶ This highlights on one hand the importance of validated efficient screening strategies with US and on the other hand the need for prompt diagnosis when facing a suspicion of ruptured AAA in the ED.⁷⁷ POCUS performed by EP for AAA screening was found to be highly accurate in a meta-analysis of 7 studies (655 patients), with a sensitivity of 99% (95% confidence interval [CI] : 96% - 100%) and a specificity of 98% (95% CI : 97% - 99%) when compared to gold standard (CT-scan), magnetic resonance imaging, aortography, official US performed by radiology, EP US reviewed by radiology, exploratory laparotomy, or autopsy results).⁷⁸ In the primary care setting similar results for AAA screening have been published in yet smaller studies.^79,80 Less is known regarding the diagnostic accuracy of POCUS for the detection of ruptured AAA; performance might be lowered by the fact that AAA rupture is often retroperitoneal and thus uneasy to visualize with US.⁸¹ Nevertheless, thanks to the recognized POCUS performances in AAA and abdominal free fluid identification, POCUS for ruptured AAA diagnosis has been integrated in multimodal protocols of bedside ultrasound in acute circulatory failure (e.g. RUSH protocol, see below in chapter 2.2).⁸²

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2.1.4 Veins

Deep venous thrombosis (DVT) detection is important to POCUS multimodal approach of the patient with acute circulatory failure, in particular if pulmonary embolism is a diagnostic option.⁸² Ultrasound guided compression of the common femoral vein and the popliteal vein - namely 2-point compression - is the chosen POCUS technique to search for DVT. This examination performed by EP has shown results similar to those obtained by radiologists, with sensitivity of 91% (CI 95% = 68–98%) and specificity of 98% (CI 95% = 96–99%) for the diagnosis of DVT in a recent meta-analysis.^83,84 Similar results with DVT diagnostic accuracy of >95% were obtained in primary care with general practitioners given short training.⁸⁵

POCUS guided catheterization of central and peripheral veins is a highly studied field that is described in section 2.3 (procedure guidance).

A few other POCUS diagnostic applications are regularly cited (e.g. eye, evaluation of fracture of the limbs and other musculoskeletal disorders) but are not part of the core usual POCUS activity in IM and EM. They are mentioned in Table 1 but are not described in details in this review.

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2.2 Acute distress syndromes

Acute distress syndromes (ADS) can be life threatening and occur regularly in IM and EM. Some of them are accessible to POCUS evaluation; in these situations POCUS of multiple systems (e.g. heart and lungs) is performed within a short period of time in order to guide and improve initial critical treatment strategy. Multimodal POCUS in such circumstances typically requires various focused ultrasound skills that should be mastered by internists and EP to optimize therapy. The main ADS and their corresponding multimodal POCUS protocol are listed below and will be described in details in this section:

 Multiple trauma and E-FAST (Extended- Focused Assessment with Sonography in Trauma) protocol

 Acute respiratory failure and BLUE (Bedside Lung Ultrasound in Emergency) protocol

 Acute circulatory failure RUSH (Rapid Ultrasound in SHock) protocol

 Cardiac arrest CAUSE (Cardiac Arrest UltraSound Exam) protocol

2.2.1 Multiple trauma and E-FAST protocol

E-FAST, exclusively used in the ED, deserves a particular attention in our review since it stands as a milestone in POCUS history; it was the first bedside ultrasound protocol, dedicated to the evaluation of blunt trauma patients with POCUS. FAST was developed in the late 1990’s by surgeons to identify intra-abdominal free fluid (FF) and pericardial effusion (PEf) in trauma patients while older more invasive techniques like diagnostic peritoneal lavage were declining.¹⁵ Fifteen years ago FAST evolved to E-FAST (Extended-FAST) with the adjunction of pleural ultrasound windows to detect PTX and hemothorax.¹⁶ Diagnostic accuracy of E-FAST in trauma patients was assessed in a recent meta-analysis of 75 studies (24350 patients) examining E-FAST detection of PTX (n = 17), PEf (n = 9) and FF (n = 52);

pooled sensitivities and specificities were calculated for the detection of pneumothorax (69% (95%

confidence interval 0.660–0.727) and 99% (95% CI 0.99–0.99) respectively, gold standard = CT-scan), PEf (91% (95% CI 0.870–0.944 and 94% (95% CI 0.922–0.957) respectively, gold standard = CT-scan or positive intra-operative findings), and intra-abdominal free fluid (74% (95% CI 0.726–0.758) and 98%

(95% CI 0.973–0.978) respectively, gold standard = positive laparotomy findings, diagnostic peritoneal lavage/aspirate, or CT-scan).⁸⁶ Except for the detection of PEf in which POCUS showed excellent global accuracy, these results remind us that EFAST exhibit primarily excellent specificity but it is not a fully reliable tool in terms of sensitivity and thus does not allow to “rule out” post-traumatic bleeding and/or PTX; CT scan should then be readily considered in case of negative POCUS findings, even if some data

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indicate that reducing CT use by systematically performing clinical examination and E-FAST in multiple trauma might be safe.⁸⁷ In terms of proven clinical benefits, while no data demonstrate effects on survival, E-FAST has been shown to significantly reduce time to operative care (57 minutes with E-FAST vs 166 minutes without E-FAST) in patients needing emergent surgery in a randomized (EFAST vs usual care) study of patients with suspected torso trauma. This study also suggested reduced CT scan use, complications and LOS in the E-FAST group.⁸⁸ In addition, in a retrospective recent study, the use of E- FAST as initial assessment had a therapeutic impact in 10% of 756 severe trauma patients leading appropriately (appropriateness = 98.7%, 75/76) to immediate laparotomies and chest tube insertions.⁸⁹ For these reasons E-FAST protocol is currently supported by the Advanced Trauma Life Support providers and used around the world in EM.^16,90

2.2.2 Acute respiratory failure and the BLUE protocol

Acute respiratory failure (ARF) is a very common clinical and critical condition in IM and EM. As mentioned above in chapter 2.1, POCUS exhibits convincing diagnostic accuracies in numerous individual etiologies of ARF such as heart failure, pneumonia, pneumothorax and pulmonary embolism for example. Over the years, mixing various POCUS applications became obvious facing complex clinical pictures such as ARF. Thus combination of pleuro-pulmonary and vein POCUS applications resulted in the development of the Bedside Lung Ultrasound in Emergency (BLUE) protocol. This protocol basically integrates POCUS views aiming at detecting lung sliding, A and B lines, lung point, signs of pneumonia/consolidation (here called “C” lines) and DVT. It is described in details in figure 12a.¹⁹ It has been shown effective in identifying the underlying cause of ARF in 90.5% of 260 intensive care patients retrospectively analyzed.⁵² In addition, BLUE protocol combined with heart POCUS was compared to usual care in a large prospective randomized study of 320 patients with ARF in the ED. In the POCUS arm, the proportion of correct diagnosis within the first 4 hours of admission shifted from 64% (CI 56·1- 71·3) to 88% (95% CI 82·8-93·1), though without additional demonstrated benefits on “harder” clinical endpoints (LOS, 30-day readmission and mortality), for which this study was not powered.⁹¹ The International Consensus Conference on Lung Ultrasound consequently stands as a strong support to POCUS use in ARF.⁴¹

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Figure 11. a–c The BLUE, RUSH and CAUSE protocols. Reproduced with permission of

Internal Medicine and Emergency Journal, Leidi A and Grosgurin O

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2.2.3 Acute circulatory failure and the RUSH protocol

Acute circulatory failure (ACF) has numerous potential underlying pathophysiological mechanisms, such as hypovolemia (e.g. hemorrhage), cardiogenic dysfunction (e.g. acute myocardial infarction), vasoplegia (e.g. anaphylaxis, sepsis) or obstruction (e.g. tamponade, massive pulmonary embolism).

Early detection and appropriate initial therapy of ACF are crucial to preserve adequate organ perfusion.

As it is the case in ARF, mixing various POCUS applications has the potential to supplement physical examination in the evaluation of the different key circulatory parameters; indeed, as mentioned earlier, POCUS allows a reliable evaluation of left ventricular global function, right ventricular enlargement, pericardial fluid, hypovolemia, DVT and ruptured abdominal aortic aneurism. Combining these applications led to the development of structured protocols, like the Rapid Ultrasound in SHock (RUSH) protocol evaluating the cardiac status (pump), the fluid status (tank) and the vascular status (pipes).⁸² This protocol is detailed in figure 12b. This protocol was evaluated in a randomized trial performed in the ED: 184 patients with undifferentiated ACF received either immediate POCUS or usual care. The median number of viable physician diagnoses at 15 minutes was reduced in the POCUS group compared to the usual care group (4 vs 2, p<0.0001). The rate of final correct diagnosis was also markedly higher in the POCUS group (80% (95% CI : 70–87%) versus 50% (95% CI: 40–60%)).⁹² In an observational study conducted in the ED, a convenient sample of 118 patients with undifferentiated hypotension was evaluated with multimodal POCUS. After POCUS assessment, definite cause of hypotension was raised from 0.8% to 12.7% (+11.9%; 95% CI: 5.6–18.1) and there was a 27.7% relative decrease of global diagnostic uncertainty among ED physicians (mean aggregate complexity of diagnostic uncertainty before and after: 1.85-1,34, p<0.0001). In addition, treatment and major imaging plan were changed after POCUS completion in 24.6% and 30.5% of cases, respectively.⁹³ The majority of available data regarding POCUS in respiratory and circulatory failure are obtained from emergency or critical care departments. Interestingly a very recent additional study was conducted on hospital wards; internal medicine and surgical ward patients presenting acute respiratory and/or circulatory failure were evaluated by a rapid response team (critical care providers) with or without POCUS. The POCUS protocol included focused cardiac US, LUS and US search for DVT when appropriate. In this prospective observational controlled trial, the rapid response team used this POCUS protocol every other day during the study period (control group = without POCUS). The proportion of immediate adequate diagnosis at the bedside was 94% in the POCUS group versus 80%

in the control group (p=0.009). Statistically significant results were also noted for secondary objectives, such as reduced time to diagnosis and mortality.⁹⁴ Finally, only one multicenter randomized controlled trial assessed the effect of POCUS strategy in terms of clinical benefits in undifferentiated shock. This

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trial included 270 patients and failed to show benefits in mortality and LOS, but it should be reminded that it could not reach its inclusion objectives and thus it was considered underpowered.⁹⁵ Despite this underpowered trial with neutral results, other trials have shown the added value of POCUS making it an integral part of the recommended diagnostic strategy in ACF.¹⁴

2.2.4 Cardiac arrest and the CAUSE protocol

In cardiac arrest (CA) prognosis is dark despite progress in basic and advanced cardiac life support, with survival rates between 10 and 17%.⁹⁶ Among factors associated with better survival in CA, shockable rhythm (ventricular fibrillation, pulselessness ventricular tachycardia, torsade de pointe) stands out with OR 5.28 for survival (95% CI : 3.78-7.39) in a recent meta-analysis pooling 23 studies.⁹⁷ The vast majority of patients suffering from in-hospital CA (80%), however, present with non-shockable rhythms.⁹⁸ In these circumstances it is particularly recommended to try to identify potential reversible CA etiologies such as 5H’s (hypoxemia, hypovolemia, hyper/hypokaliemia, hypothermia, H+ (acidosis)) and 5T’s (tamponade, tension PTX, pulmonary or coronary thrombosis and toxins).⁹⁹ POCUS is recognized as a reliable tool to suspect or identify four of the above mentioned etiologies. The Cardiac Arrest Ultrasound Exam (CAUSE) is a structured pleuro-pulmonary and cardiac POCUS protocol that was tailored to CA evaluation (figure 12c).¹⁰⁰ CAUSE protocol allows identification and immediate treatment (e.g. pericardiocentesis) of potentially reversible causes of CA and thus may improve survival rate in these patients, even though it has never been proven. In addition, the prognostic contribution value of POCUS in CA has been studied. In 793 patients with non-shockable CA, survival to hospital discharge was 0.6% (3/530) when no cardiac wall motion was seen with POCUS during pulse check, compared to 3.8% (10/263) when wall motion was present.¹⁰¹ In another study enrolling 169 patients, the absence of cardiac motion during CA was associated with a positive predictive value of 100% for mortality (negative predictive value for mortality = 58%), irrespective of the initial rhythm.¹⁰² These convincing data indicate that POCUS may contribute, with other prognostic parameters, to the decision process regarding discontinuation of resuscitation. However, questions have been raised regarding the absence of uniform definition of cardiac wall motion, the scarcity of well conducted studies regarding POCUS prognostic factors in CA and the uncertainty of inter-rater reliability of POCUS in CA. This recently led adult advanced life support experts to recommend against the use of POCUS for prognostication in CA until more convincing data is available.¹⁰³ Conversely, the recent consensus of the international federation for EM recommends POCUS in CA, provided that brief imaging acquisition is performed during pulse check to minimize chest compression interruptions, with the reviews of saved video clips during the next compression cycle.¹⁰⁴

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2.3 Procedure guidance

In their daily practice internists and EPs perform several invasive diagnostic and/or therapeutic procedures. POCUS guidance of these procedures has established benefits for patient care in terms of success rate and safety and has thus become the standard of care. Data and guidelines regarding some of these commonly POCUS-guided procedures are presented in the following sections.

2.3.1 Central venous catheterization

The insertion of a central venous line (CVL) in the internal jugular vein using anatomical landmarks can be unsuccessful and/or can lead to significant complications (arterial puncture and/or cannulation, hematoma, hemothorax, or pneumothorax) in a significant proportion of patients.¹⁰⁵ The rationale for using POCUS to minimize these risks relates to its ability to identify anatomic venous variations or thrombosed jugular vein (due to oncologic disease for example) and confirm intravenous catheter placement at the end of the procedure (figure 13). The added value of POCUS in jugular CVL placement have been extensively studied over the last decades. In a meta-analysis of 35 randomized studies (5108 patients), the use of POCUS for jugular CVL placement raised the success rate by 12% (RR 1.12, 95% CI 1.08 - 1.17; p < 0.00001, absolute success rate 97.6% versus 87.6%) and reduced the rate of total complications by 71% (risk ratio (RR) 0.29, 95% confidence interval (CI): 0.17 - 0.52; p < 0.0001, absolute risk 13.4% versus 3.9%). In addition, the number of attempts required for successful jugular vein catheter insertion was decreased (mean difference -1.19 attempts, 95% CI: -1.45 - 0.92; p <

0.00001).¹⁰⁶ These convincing results led acute medicine societies (anesthesiology, EM, critical care medicine (CCM)) to strongly recommend POCUS use for jugular CVL placement.^14,107-109 This practice is recognized as essential for this procedure and is now undoubtfully integrated as a standard of care in every center where CVL placement is performed.

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Figure 13. POCUS confirmation of intraluminal venous position of CVL. Reproduced with permission of the original publisher BioMed Central (BMC), Saugel et al,

White arrows: intraluminal CVL on short (left) and long (right) axis

2.3.2 Peripheral venous catheterization

Insertion of a peripheral venous line (PVL) can be challenging and has revealed unsuccessful in up to one fourth of cases using conventional “blind” technique. Several factors influence the success rate, including nurse experience, “rolling veins” and tough or dark skin.¹¹⁰ Following the development of POCUS-guided CVL placement clinicians began to translate this ultrasound-guidance model to PVL insertion in the beginning of the early 2000’s. Since then multiple studies confirmed the benefits of POCUS-guided PVL insertion: for patients identified with difficult peripheral venous access, a meta- analysis pooling the results of 7 studies showed that ultrasound guidance improved the success rate of PVL placement when compared to conventional technique (OR 3.96; 95% CI: 1.75-9.94).¹¹¹ POCUS is now widely adopted for difficult PVL placement and improves patients care in this domain, provided that key practical aspects regarding veins selection, catheter selection and the technique itself are respected.¹¹²

2.3.3 Thoracentesis and paracentesis

Thoracentesis and paracentesis are both performed very frequently in IM and EM. PTX and abdominal hemorrhage have been identified as rare but serious complications of thoracentesis and paracentesis, respectively.^113-115 As mentioned in section 2.1.2.3 and 2.1.3.1 POCUS reliably detects pleural and peritoneal fluids. Increasing use of POCUS over the years to assist the drainage of these free fluids has logically followed the ultrasound-guidance movement initiated with intravenous line placement. A very large observational study analyzed the outcome of 61,261 thoracentesis and 69,859 paracentesis,

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for which POCUS-guidance use rate was 45%. Although overall absolute complication occurrence was low in this study, ultrasound-guided versus conventional procedure diminished PTX risk after thoracentesis by 19% (OR, 0.81; 95% CI: 0.74-0.90, absolute risk 2.26% versus 3.09%) and bleeding complications after paracentesis by 68% (OR, 0.32; 95% CI: 0.25-0.41, absolute risk 0.27% versus 1.25%). Though still speculative, POCUS is likely associated with a decreased LOS and costs, since complications were significantly associated with increased LOS and costs in this study.⁶⁶

POCUS guidance of thoracentesis and paracentesis can be performed with one of these two following techniques. In the “marked” technique, the location of fluid is identified with POCUS first, marked on the patient’s skin and only thereafter paracentesis is performed but without ultrasound. In the “real time” technique ultrasound control is maintained throughout the whole procedure (fluid identification, needle visualization, immediate detection of post-procedural PTX after thoracentesis).

Regarding thoracentesis a recent retrospective study compared these two techniques in 394 ICU patients, showing that the“real time” technique was associated with lower rates of iatrogenic PTX (0.63%; 95% CI: 0.11–3.4% vs 4.43%; 95% CI: 2.35–8.21%, p = 0.02).¹¹⁶ In paracentesis, even if no comparison between the two techniques has been performed, “real time” technique also showed extremely low risk of hemorrhage requiring transfusion (0.19%) in more than 3000 cirrhotic patients.¹¹⁷ POCUS guidance for thoracentesis and paracentesis is now widely recommended, with a preference for the “real time” technique, in particular for thoracentesis.^118,119

2.3.4 Lumbar puncture

Lumbar puncture (LP) failure rate is about 20% when conventional anatomical landmarks are used. LP failure rate is especially high (50% of the failed LPs) in patients with body mass index (BMI) >35.¹²⁰ By selecting the widest interspinous space US can identify the insertion site with the highest chance of successful LP. Additionally US allows the measurement of the distance from the skin to the ligamentum flavum (LF), thus allowing to select an appropriate catheter length and to predict needle insertion depth to obtain cerebrospinal fluid (CSF).¹²¹ A US longitudinal image of the spine allows visualization of interspinous space and LF, thus indicating the way to CSF (figure 14). As with paracentesis and thoracentesis, “real time” procedure can be performed but the most common technique of ultrasound guidance for LP is marking the needle insertion site using static ultrasound.¹²¹ As in many POCUS applications, unexperienced EPs can obtain high quality sonographic images after very limited training.¹²² New techniques are emerging, using electromagnetic needle guiding system allowing 3D

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visualization of the needle way in the tissue and may further improve success and safety of LP in the future.¹²³

Figure 14. Ultrasound guidance of LP, longitudinal midline view. Reproduced with permission of Neurology Clinical Practice, Soni et al

The transducer is centered over a lumbar interspinous space in a longitudinal plane, and a mark is made perpendicular to the center of the transducer. The spinous processes (SP) and interspinous spaces (*) are visualized in a longitudinal plane, and the ligamentum flavum (LF) and posterior longitudinal ligament (PLL) are visualized deep to the spinous processes.

Many studies have evaluated the benefits of US-guided LP. Recently a meta-analysis pooled the results of 14 randomized studies (1334 patients) comparing US imaging to the reference landmark technique in LP and epidural catheterization. US guided procedure reduced the risk of failure (risk ratio 0.21 (95%

CI: 0.10-0.43), p<0.001, absolute risk 0.9% versus 7.2%, number needed to treat = 16) in both LP and epidural catheterization. In addition, US reduced the risk of traumatic procedure (risk ratio 0.27 (0.11 to 0.67), p = 0.005, number needed to treat = 17), the number of insertion attempts (mean difference

−0.44 (−0.64 to −0.24), p < 0.001), and the number of needle redirections (mean difference −1.00 (−1.24 to −0.75), p<0.001).¹²⁴ These convincing results led to strong recommendations for the use of US to assist LP, particularly in obese patients.¹²⁵

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2.4.5 Other procedure guidance

Although crucial, acute pain treatment is sometimes difficult and systemic analgesics have their limits in terms of side effects. Nerve blocks thus play a key role in pain management in certain indications.

Ultrasound can efficiently guide nerve blocks and this technique is progressively integrated in a growing number of Emergency Departments. For example, briefly trained EP were shown to perform safe and effective US-guided femoral blocks after proximal femur fracture: effective pain control was obtained at 60 minutes in 83.3% of 64 patients in a recent uncontrolled study.¹²⁶

Guidance of basic arthrocentesis is another domain where POCUS might be helpful for internists and EPs. Recently US-guided knee arthrocentesis was compared to conventional landmark technique. EPs randomized 66 patients to US-guided versus conventional procedure. Success rate was similar in both groups (US-guided 37/39 vs. LM 25/27); p = 1.0), but physicians felt the US-guided procedure was easier to perform and the total procedure time was shorter in the US group.¹²⁷ Similar results were found in an emergency physician study for hip, ankle and wrist joints aspiration in cadavers.¹²⁸ Another study found that success rate of knee arthrocentesis was 100% in the US-guided group versus 82% in the landmark group (p=003).¹²⁹ These encouraging results should be confirmed in larger studies, ideally with an RCT design, and should stimulate the extension of US-guidance to all regularly aspirated joints.

In conclusion of this chapter, POCUS demonstrated benefits are principally related to straightforward diagnoses and various procedure guidance. As further discussed in chapter 4 (section n4.5), much less is scientifically known about the impact of POCUS on clinical outcomes.

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3. POCUS training

As described with existing studies in the preceding chapters, POCUS efficiently extends physical examination and improves diagnostic and treatment in various domains and procedures. POCUS research and practice nevertheless remains challenging and challenged: POCUS providers might sometimes be underrepresented in their departments and/or insufficiently trained, with consequent inhomogeneous and/or inadequate POCUS levels of competencies. This highlights the need for ongoing and future rigorous POCUS training and implementation; both these parameters are intimately linked in practice. For didactic reasons they are presented separately in this review, POCUS training being approached here and implementation in the next chapter.

In this chapter and manuscript, training to reach POCUS basic level is described in details, even though two other levels of POCUS exist : the minimal level (bladder distension and procedure guidance for example, affordable for all clinicians after minimal training) and the advanced level, the latter being often aimed by advanced providers but without homogeneous objectives nor proper certification yet (table 2).

Table 2. Different levels of POCUS training

Minimal level Minimal theoretical course

Minimal bedside formation

Basic Level Basic initiation (theory and hand’s on practice)

Basic practical training Basic certification (SGUM*)

Advanced Level Advanced theoretical course

Advanced practical course

* see chapter 4.6

3.1 POCUS basic general training structure

Given the youth of POCUS and the growing number of disciplines aiming at mastering it, POCUS training is becoming a major teaching challenge. In acute medicine (mainly EM, IM and CCM)) a basic training

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structure has been built over the years and is generally followed by institutions promoting POCUS implementation, even if educational methods and means vary a lot. It is presented in figure 15.

3.1.1 POCUS initiation

POCUS initiation includes POCUS theory delivery and novice practical “hands on” US sessions. US theory has traditionally been delivered through formal face-to-face teaching along with dedicated educational material. The important faculty teaching cost of this large volume of theory (in general 10- 20 hours depending on the POCUS program) and the obvious lack of uniformity associated with this teaching strategy led numerous institutions to re-think POCUS teaching methods. Web-based teaching has logically emerged as a key alternative, offering educational content standardization, enhanced accessibility and flexibility for participants.¹³⁰ In addition it was shown to be highly effective for the acquisition of basic POCUS knowledge, not only in terms of test scores but also regarding organizational and logistical investment.^131-133 It is thus progressively becoming a standard teaching method for POCUS initial theory teaching delivery.

Initiation to US “hands on” practice is crucial and should closely follow POCUS theory teaching, thus favoring the anchorage of recently acquired knowledge. Above mentioned Web-based teaching has decongested POCUS initiation courses: more “live” time is thus available for practice teaching, offering more intense technical and image-centered implication of participants. This teaching usually lasts one day (duration depends on the number of targeted applications) and is generally delivered with an expert to student ratio of 1 to 3-4.¹³⁴ Ultrasounded subjects are usually live healthy models, but can also be hospitalized patients, especially in internal medicine where longer stay can easily offer this opportunity that is highly valued by participants.^134,135 A this stage high fidelity manikins progressively have a growing place in POCUS training since they can reliably mimic numerous pathologies and serve as a complement to practice with real patients. POCUS initial teachers are most of the time faculty US certified physicians of the POCUS discipline, but interprofessional models where teaching is delivered by diagnostic medical sonography (DMS) students have shown promising results and could broaden the circle of eligible US teachers,¹³⁶ which is a major concern in POCUS teaching and implementation.

Even though tutor-based practical “hands on” direct teaching and supervision with immediate human feedback on live subjects is deservedly considered the most adequate teaching method, simulation- based training using a mock transducer showed promising results in focus transthoracic echocardiography training,¹³⁷ in particular for institutions with slow development of POCUS experts teams.